Ferromagneticpiezoelectric ceramic composition

ABSTRACT

A piezoelectric ceramic composition which comprises the combination of a pyrochlore composite oxide Ba 2  Sb 2  O 7 , and a base ceramic mixture of PbTiO 3  and PbZrO 3 .

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation, of application Ser. No. 709,714, filed July 29,1976, now abandoned which is a continuation-in-part application Ser. No.420,653, filed Nov. 30, 1973, now U.S. Pat. No. 4,087,366.

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

This invention relates to a piezoelectric ceramic composition. Moreparticularly, it relates to a piezoelectric ceramic composition whichhas improved dielectric and piezoelectric characteristics.

2. DESCRIPTION OF THE PRIOR ART

Barium titanate type ceramic compositions and lead zirconate-titanatetype ceramic compositions have been used as piezoelectric ceramiccompositions. These compositions, however, are not stable industrialcompositions. Therefore, efforts have been directed to developingimproved piezoelectric compositions. One of these improved compositionsis a ternary system of a solid solution of Pb(Mg_(1/3).Nb_(2/3))O₃-PbTiO₃ -PbZrO₃. It has also been proposed to modify and improve thepiezoelectric properities of the composition by the addition of an oxideof Mn, Cr, Co, Fe or Ni to the basic composition. One of the problemswith this composition is the moisture absorbing property of thecomposition containing Mg which interfers with accurate weighing of thecomposition and the storage of the starting materials. Although thecomposition has an electromechanical coupling coefficient, Kp of 50-58%,the dielectric loss of the composition is as high as 2-2.4%.

In the ternary solid solution of the base ceramic components of PbTiO₃-PbZrO₃ and the additive, Pb(Mn_(1/3) Sb_(2/3))O₃, the dielectricconstant ε and the electro-mechanical coupling coefficient Kp are easilychanged by small changes in the components. Compositions having Kpvalues greater than 50% have low dielectric constants of about 500.Since compositions having a dielectric constant greater than 1000 havebeen limited to rather narrow ranges of the components, the number ofindustrially suitable piezoelectric has been limited to a relative few.The compositions of the prior art have been combinations of the abovebase ceramics components and a perovskite type component, ABO₃.

Other proposed improvements for the compositions have involved theaddition of certain additives to the base ceramic components of PbTiO₃-PbZrO₃. For example, in one procedure, the basic ceramic compositionhas been modified by substituting Pb by Sr and by the addition of acomponent Sb₂ O₃ and MnO₂. Up to the present, the most effectivemodified piezoelectric composition has been one whose base ceramiccomponents of PbTiO₃ and PbZrO₃ are in a ratio of 47:53 and which hashad values of Kp=60%, ε=1750 and tan δ=2.5%. However, these compositionshave had the disadvantage that their performance characteristics arereadily changed by the small changes in their component structure. Forexample, a change in the quantity of Mn of 0.15 wt. % causes a change ofQm from about 1170 to about 300. If it is desired to decrease the tan δvalue to 1.0% by adding another component, the value of Kp changes from60% to 4.83%. To the present, piezoelectric ceramic compositions havingthe desired combination of Kp, ε, Qm and tan δ values which are stableto small changes in the component makeup of the composition have notbeen obtained.

A need therefore, continues to exist for piezoelectric compositionswhich have Kp, ε, Qm and tan δ values which are stable to small changesin the component makeup of the compositions, and which have highpiezoelectric constants.

SUMMARY OF THE INVENTION

Accordingly, one object of the invention is to provide a piezoelectricceramic composition having a high piezoelectic consant and stabilitywhich has an optimum balance of the electro-mechanical couplingcoefficient Kp, the dielectric constant ε, the mechanical quality factorQm and the low dielectric loss factor tan δ.

Another object of the invention is to provide a piezoelectric ceramiccomposition having a high stability to applied voltages and high flexstrength which has improved dielectic and piezoelectric characteristics.

Yet another object of the invention is to provide a piezoelectic ceramiccomposition which is useful as a high power ultrasonic transducer inwater or as a wide band filter element.

Briefly, these objects and other objects of the invention as hereinafterwill become more readily apparent can be attained by providing apiezoelectric ceramic composition which comprises the combination of apyrochlore complex oxide Ba₂ Sb₂ O₇ and a mixture of PbTiO₃ -PbZrO₃ceramic components.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconidered in connection with the accompanying drawings, wherein:

FIG. 1 is a partial view of the triangular coordinate of the ternarysystem solid solution of the invention;

FIGS. 2A and 2B are graphs showing the relationship of dielectricconstant and dielectric loss, respectively versus terminal voltage ofseveral piezoelectric compositions including some prior artcompositions;

FIG. 3 is a graph showing the relationship of mechanical quality factor(Qm) versus terminal voltage of several piezoelectric compositionsincluding some prior art compositions; and

FIG. 4 is a graph showing the relationship of amplitude (μ) versusterminal voltage of several piezoelectric compositions including someprior art compositions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The piezoelectric ceramic, solid solution composition of the inventionhas the following characteristics: Kp of 60% to 74.5%, ε of about 1000to 1800 and a tan δ value of less than 0.3%.

Pyrochlore type composite oxides which the present composition containshave complicated structures having 8 structural units per unit cell. Inaddition, the SbO₆ component of the pyrochlore oxide has zig-zag chainsof O--Sb--O and one oxygen atom which is bounded by four barium atoms.The latter group is independent of the Sb atom. When the pyrochlore typecomposite oxide of Ba₂ Sb₂ O₇ is combined with the base ceramiccomponents of PbTiO₃ and PbZrO₃ and the mixture is sintered at atemperature greater than 1000° C., a piezoelectric ceramic compositionhaving the following formula is formed:

    x(Ba.sub.2 Sb.sub.2 O.sub.7).sub.1/2.(1-x)[yPbTiO.sub.3.zPbZrO.sub.3 ]

wherein 0.51≦y≦0.47, 0.49≦z≦0.53, y+z=1.0 and 0.01≦x≦0.07, preferably0.50≦y≦0.48, 0.50≦z≦0.52, y+z=1.0 and 0.02≦x≦0.05. The mixture ofpyrochlore composite oxide and the ceramic component can be calcinedbefore it is sintered. Preferably, Mn is added to the composition asMnO₂ in quantities of 0.1-1.0 wt.%, preferably 0.3 to 0.7 wt.% relativeto the total basic components. FIG. 1 is a triangular coordinate systemof the ternary solid solution x(Ba₂ Sb₂ O₇)_(1/2).(1-x) [yPbTiO₃.zPbZrO₃] of the invention.

The compositions of the invention which are suitable for broadapplications and practical uses, have ratios of PbTiO₃ to PbZrO₃ of46-54:54-46 mole % and Pb(Ti.Zr)O₃ to (Ba₂ Sb₂ O₇)_(1/2) ratios of99-93:1-7 mole %.

The compositions, have Kp values greater than about 60%, ε valuesgreater than about 1000 and tan δ of less than 0.3%. The piezoelectricproperties of the compositions are continuous in the range of 1-7 mole %of (Ba₂ Sb₂ O₇)_(1/2), so that the stability of the composition isremarkably high as shown in Table 2.

When Mn is present in the composition, the mechanical quality factor Qmcan be increased to about 1800 to 3200 and the dielectric loss tan δ isdecreased to less than 0.3 %. However, the dielectric constant and theelectromechanical coupling coefficient do not fluctuate much, so that aremarkable combination of characteristics of Kp, ε, tan δ and Qm can beobtained. Thus, the composition can be readily mass produced.

The improved characteristics exhibited by the compositions of theinvention fluctuate only very slowly when the amounts of the componentsare altered because the complex pyrochlore oxides having long-rangeforces which are characteristic of the pyrochlore oxides. They are verydifferent from the ABO₃ type compounds.

The ferroelectric piezoelectric ceramic compositions of the inventionhave the characteristics of being continuously stable while showing onlyslight fluctuations of the characteristics when the components of thecompositions are changed only slightly. Thus, the industrial advantagesfor these compositions are substantial.

The combined characteristics of the compositions of the invention arevery good, and as a result, the dielectric characteristics exhibit ahigh degree of stability to changes of the applied voltage. Incomparison to the low stability of the conventional compositions, thesolid solutions containing the pyrochlore complex oxides of theinvention have remarkable stability.

The important feature of the invention is to separately preparepyrochlore composite oxide Ba₂ Sb₂ O₇ and the basic ceramic componentsof PbTiO₃ and PbZrO₃ and then they are admixed together with a manganesecomponent and the mixture is sintered. It is preferable to calcine themixture of the pyrochlore composite oxide and the basic ceramiccomponents of PbTiO₃ and PbZrO₃ and manganese oxide and then to crushthe calcined mixture and to mold the powder of the calcined mixture andto sinter the molded mixture. The mixture of the pyrochlore compositeand the basic ceramic components of PbTiO₃ and PbZrO₃ and manganeseoxide is sintered at higher than 1000° C. and usually at 1000° to 1300°C. preferably 1000° to 1200° C. whereby the pyrochlore composite isfirstly melted to form the liquid phase and the basic ceramic componentsof PbTiO₃ and PbZrO₃ are converted in the liquid phase of the pyrochlorecomposite to form the piezoelectric ceramic composition.

Since the components of the pyrochlore composite and the basic ceramiccomponents are sintered, the form of solid solution is different in thesintering step.

Since the basic ceramic components are converted in the liquid phase ofthe pyrochlore composite, in the sintering step, fine grains such asless than 5μ especially 1.0 to 2.5μ of a diameter are formed and thegrain boundary contains higher content of impurities.

When the solid phase reaction for all components is performed, the grainsize is too large and a desirable product can not be obtained. When allcomponents are melted at once in the sintering step a desirable productcan not be obtained. When the pyrochlore composite is firstly melted andthe basic ceramic components of PbTiO₃ and PbZrO₃ are converted, thefine grain size product can be obtained. The additive of manganese oxideis important for improving the characteristics of the product. Thedegrees of variations of the characteristics of Qm, εv/ε, and tan δdepending upon change of terminal voltage applied to the products arerelatively decreased by the addition of the manganese oxide for exampleas stated in the examples. It is preferable to obtain a product whichhas low variations of characteristics under change of voltage appliedespecially in high voltage.

The fact can be considered as good linearities of the outputcharacteristics depending upon change of the input.

When the grain size is decreased, the mechanical strength of the productis increased. When the pyrochlore composite is not preliminarilyprepared by the calcination of the raw materials and only the componentsof barium oxide and antimony oxide are mixed without preparing thepyrochlore, the liquid phase of the pyrochlore is not formed in thesintering step and it is impossible to form fine grains.

The advantages of the piezoelectric ceramic composition of the inventionare attained by the formation of the fine grains resulted by the liquidphase conversion and the effect of manganese oxide to decrease thedegrees of variations of characteristics depending upon change ofvoltage applied.

When the piezoelectric ceramic compositions are used in an ultrasonictransducer, the input load increases in the generation of high powerultrasonic waves. The stability of the dielectric loss (tan δ)-voltagecharacteristics is important in this regard.

An increase in the tan δ value means an increase in the amount of heatwhich is not desirable. The mechanical quality factor Qm which is in areciprocal relationship to tan δ, is also very stable to changes in thevoltage.

FIGS. 3 & 4 shows the relationship of the mechanical quality factor Qmof a bolt fitted Langevin transducer (30 mm diameter) and the amplitudeμ under non-loaded conditions in air, which shows excellent overallpiezoelectric characteristics with excellent dielectric characteristics.

When a conventional transducer is resonated in a range of 0-30 volts,the transducer shows a sudden decrease in the mechanical quality factorQm at about 10 volts, and the amplitude is limited to 3-4μ. However,transducers made of the composition of the invention show a highstability for the mechanical quality Q factor as shown in FIG. 3. Withthese transducers it is possible to transduce forcibly at a level of 50volts to generate high intensity ultrasonic power. Also, the transducerdoes not deteriorate with increasing applied voltages. Since the solidsolutions of the invention contain the pyrochlore complex oxides, theyexhibit stability to applied voltages which is a fundamentalcharacteristic of the pyrochlore oxides. If the solid solutions containfrom 1.0-7.0 mole % of the pyrochlore complex oxide, they exhibit thedesired fundamental characteristics of the pyrochlore oxide.

When the temperature coefficient of the dielectric constant ε-T.C. ishigh and the piezoelectric ceramic composition itself is heated, changesin the dielectric constant ε increase while the impedance changes whichmeans that the impedance matching deteriorates and, accordingly, themaximum amplitude cannot be attained. However, the piezoelectric ceramiccompositions of the invention have excellent temperature efficiency.

The piezoelectric ceramic compositions of the invention have suitablepiezoelectric characteristics as ultrasonic transducers. The compositionof the invention can also be effectively used in various elements suchas ceramic filters, accelerameters, pick-ups and the like, withoutlimiting the effectiveness of the ultrasonic transducer as the threecomponents of the composition are varied or as the amount of manganeseadditive is varied.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

REFERENCE EXAMPLE 1

PbO, TiO₂, ZrO₂, BaO and Sb₂ O₅ were used as the starting powderymaterials for the preparation of a piezoelectric ceramic composition.(Sb₂ O₃ can be used instead of Sb₂ O₅ in equimolar amounts.) Thestarting powdery materials were weighed and mixed to provide the Ba₂ Sb₂O₇, PbTiO₃, and PbZrO₃ components. The mixed starting powdery materialswere mixed well in a separate ball mill and the mixture was molded andcalcined at about 900° C. The resulting Ba₂ Sb₂ O₇, PbTiO₃ and PbZrO₃components were weighed and mixed to provide compositions with theatomic ratios of x, y, z shown in Table 1. The mixture was furthercrushed, mixed by a ball mill and was molded under pressure of 1.5ton/cm² to form a 20 mm diameter disc with a thickness of 1 mm. The discwas sintered at 1200°-1250° C. for 2 hours to prepare a ferroelectricpiezoelectric ceramic composition. The composition was then used as apiezoelectric element in the conventional manner. A pair of Agelectrodes was placed on both sides of the disc of the piezoelectricelement and then the disc was dipped into silicon oil at 100°-150° C. ADC voltage of 3 KV/mm was impressed across the electrodes for 1 hour topolarize them. The disc was operated for 24 hours, and in order toevaluate the piezoelectric properties, i.e., the electromechanicalcoupling coefficient (Kp) and the mechanical quality factor (Qm), theI.R.E. standard circuit method was used. The coefficient Kp wascalculated by the resonant frequency (f r) and the antiresonantfrequency (f a). The dielectric constant (ε) and the dielectric loss(tan δ) were made under a frequency of 1 KHz. The value of CTC wasmeasured as a temperature coefficient of ε.

The piezoelectric properties of various (1-x)Pb(Ti_(y).Zr_(z))O₃.x(Ba₂Sb₂ O₇)_(1/2) compositions are shown in Table 1, wherein the amounts ofthe components and the resulting compositions are shown by x, 1-x, y andz. [x(Ba₂ Sb₂ O₇)_(1/2) and (1-x)(y PbTiO₃ -zPbZrO₃) were combined toform a solid solution.] As is clear from Table 1, high electromechanicalcoupling coefficients Kp were obtained over a relatively broad range,and the optimum values of Qm, ε/ε_(o) and tan δ which are necessary forthe intended purposes of the composition vary according to the broadrange compositions selected.

                                      TABLE 1                                     __________________________________________________________________________             Mn as                         flex                                            MnO.sub.2      tan σ                                                                      Kp     (ppm/                                                                              strength                               No.                                                                              x  1-x                                                                              (wt.%)                                                                            y  z  ε/ε.sub.o                                                          (%)                                                                              (%)                                                                              Qm  ° C.)                                                                       (kg/cm.sup.2)                          __________________________________________________________________________    1-1                                                                              0.20                                                                             0.80                                                                             0   0.80                                                                             0.20                                                                             590  2.0                                                                              22.0                                                                             210 1780 930                                    1-2                                                                              0.20                                                                             0.80                                                                             0   0.50                                                                             0.50                                                                             3320 2.3                                                                              36.5                                                                             130 970  920                                    1-3                                                                              0.10                                                                             0.90                                                                             0   0.54                                                                             0.46                                                                             1530 1.9                                                                              58.9                                                                             82  1090 920                                    1-4                                                                              0.10                                                                             0.90                                                                             0   0.46                                                                             0.54                                                                             3050 2.1                                                                              61.2                                                                             70  960  930                                    1-5                                                                              0.05                                                                             0.95                                                                             0   0.60                                                                             0.40                                                                             900  1.5                                                                              36.5                                                                             100 1070 920                                    1-6                                                                              0.05                                                                             0.95                                                                             0   0.52                                                                             0.48                                                                             1890 1.9                                                                              60.2                                                                             70  990  920                                    1-7                                                                              0.05                                                                             0.95                                                                             0   0.40                                                                             0.60                                                                             920  2.2                                                                              45.5                                                                             80  1250 930                                    1-8                                                                              0.01                                                                             0.99                                                                             0   0.52                                                                             0.48                                                                             1360 1.5                                                                              68.7                                                                             75  990  930                                    1-9                                                                              0.03                                                                             0.97                                                                             0   0.47                                                                             0.53                                                                             1900 1.9                                                                              74.6                                                                             65  1100 930                                    1-10                                                                             0.03                                                                             0.97                                                                             0   0.49                                                                             0.51                                                                             2050 1.8                                                                              76.6                                                                             65  1100 930                                    1-11                                                                             0.03                                                                             0.97                                                                             0   0.51                                                                             0.49                                                                             2070 1.8                                                                              76.5                                                                             67  990  920                                    1-12                                                                             0.05                                                                             0.95                                                                             0   0.47                                                                             0.53                                                                             1850 2.1                                                                              75.2                                                                             65  1150 920                                    1-13                                                                             0.05                                                                             0.95                                                                             0   0.49                                                                             0.51                                                                             2010 2.0                                                                              74.8                                                                             65  1150 930                                    1-14                                                                             0.05                                                                             0.95                                                                             0   0.51                                                                             0.49                                                                             1950 1.9                                                                              73.4                                                                             67  1000 920                                    1-15                                                                             0.07                                                                             0.93                                                                             0   0.47                                                                             0.53                                                                             1650 2.0                                                                              72.4                                                                             80  1150 920                                    1-16                                                                             0.07                                                                             0.93                                                                             0   0.49                                                                             05.1                                                                             1880 2.0                                                                              69.5                                                                             75  1150 920                                    1-17                                                                             0.07                                                                             0.93                                                                             0   0.51                                                                             0.49                                                                             1950 1.9                                                                              66.8                                                                             75  1100 930                                    __________________________________________________________________________

EXAMPLE 2

The procedure of the preparation of Reference Example 1 was followedexcept that MnO₂ was added to the basic components. The piezoelectriccompositions were prepared and the piezoelectric properties weremeasured as shown in Table 2. As is clear from Table 2, the addition ofMnO₂ resulted in substantial improvements in the values of Qm and tan δ.

                                      TABLE 2                                     __________________________________________________________________________             Mn as                   CTC  flex grain                                       MuO.sub.2      tan δ                                                                      Kp    (ppm/                                                                              strength                                                                           size                               No.                                                                              x  1-x                                                                              (wt.%)                                                                            y   z   ε/ε.sub.o                                                        (%)                                                                              (%)                                                                              Qm ° C.)                                                                       (Kg/cm.sup.2)                                                                      (μ)                             __________________________________________________________________________    2-1                                                                              0.01                                                                             0.99                                                                             0   0.48                                                                              0.52                                                                              1680                                                                             1.8                                                                             73.5                                                                              60 1030 930  8.0                                2-2                                                                              0.01                                                                             0.99                                                                             0.05                                                                              0.48                                                                              0.52                                                                              1510                                                                             0.5                                                                             71.2                                                                              1830                                                                             1010 1050 3.8                                2-3                                                                              0.01                                                                             0.99                                                                             0.1 0.48                                                                              0.52                                                                              1440                                                                             0.3                                                                             70.8                                                                              2370                                                                             990  1130 2.2                                2-4                                                                              0.01                                                                             0.99                                                                             0.3 0.48                                                                              0.52                                                                              1320                                                                             0.3                                                                             68.6                                                                              2880                                                                             950  1210 1.8                                2-5                                                                              0.01                                                                             0.99                                                                             0.5 0.48                                                                              0.52                                                                              1280                                                                             0.2                                                                             65.2                                                                              3030                                                                             890  1275 1.5                                2-6                                                                              0.01                                                                             0.99                                                                             1.0 0.48                                                                              0.52                                                                              975                                                                              0.3                                                                             59.9                                                                              2460                                                                             930  1280 1.2                                2-7                                                                              0.01                                                                             0.99                                                                             3.0 0.48                                                                              0.52                                                                              830                                                                              0.6                                                                             52.7                                                                              1450                                                                             1050 1150 1.1                                2-8                                                                              0.01                                                                             0.99                                                                             0.5 0.47                                                                              0.53                                                                              1340                                                                             0.20                                                                            69.1                                                                              2900                                                                             800  1270 1.4                                2-9                                                                              0.01                                                                             0.99                                                                             0.5 0.49                                                                              0.51                                                                              1410                                                                             0.2                                                                             70.0                                                                              2670                                                                             800  1270 1.5                                2-10                                                                             0.01                                                                             0.99                                                                             0.5 0.51                                                                              0.49                                                                              1540                                                                             0.20                                                                            72.0                                                                              2400                                                                             900  1270 1.6                                2-11                                                                             0.03                                                                             0.97                                                                             0.5 0.47                                                                              0.53                                                                              1700                                                                             0.16                                                                            71.0                                                                              2100                                                                             1070 1280 1.5                                2-12                                                                             0.03                                                                             0.97                                                                             0.5 0.49                                                                              0.51                                                                              1770                                                                             0.16                                                                            73.5                                                                              2060                                                                             1040 1280 1.7                                2-13                                                                             0.03                                                                             0.97                                                                             0.5 0.495                                                                             0.505                                                                             1800                                                                             0.15                                                                            74.5                                                                              2000                                                                             1020 1280 1.6                                2-14                                                                             0.03                                                                             0.97                                                                             0.5 0.50                                                                              0.50                                                                              1840                                                                             0.15                                                                            74.0                                                                              1890                                                                             1050 1270 1.5                                2-15                                                                             0.03                                                                             0.97                                                                             0.5 0.51                                                                              0.49                                                                              1810                                                                             0.16                                                                            73.0                                                                              2040                                                                             1050 1270 1.5                                2-16                                                                             0.05                                                                             0.95                                                                             0.5 0.47                                                                              0.53                                                                              1740                                                                             0.20                                                                            72.2                                                                              2600                                                                             1000 1280 1.7                                2-17                                                                             0.05                                                                             0.95                                                                             0.5 0.49                                                                              0.51                                                                              1670                                                                             0.18                                                                            71.6                                                                              2520                                                                             980  1280 1.6                                2-18                                                                             0.05                                                                             0.95                                                                             0.5 0.51                                                                              0.49                                                                              1600                                                                             0.18                                                                            69.8                                                                              2700                                                                             1030 1280 1.6                                2-19                                                                             0.07                                                                             0.93                                                                             0.5 0.47                                                                              0.53                                                                              1550                                                                             0.22                                                                            68.7                                                                              2100                                                                             1200 1280 1.8                                2-20                                                                             0.07                                                                             0.93                                                                             0.5 0.49                                                                              0.51                                                                              1480                                                                             0.20                                                                            65.0                                                                              2400                                                                             1180 1280 1.7                                2-21                                                                             0.07                                                                             0.93                                                                             0.5 0.51                                                                              0.49                                                                              1410                                                                             0.20                                                                            62.8                                                                              3200                                                                             1180 1280 1.6                                __________________________________________________________________________

EXAMPLE 3

Various known or prior art piezoelectric compositions were compared toExamples 2-13 and 2-19 with regard to dielectric loss (tan δ), themechanical quality factor (Qm), εv/εo and amplitude which can bereferred to as the kinetic characteristics of a piezoelectriccomposition as a function of terminal voltage.

SAMPLE A-37

The composition of sample 37 (herein designated as A-37) of Table 4 ofUSP 3,518,199, was prepared as a reference example. PbO, TiO₂, ZrO₂, Fe₂O₃ and Sb₂ O₃ were mixed in a ball-mill in the following quantitiesindicated as mole percent.

Pb(Fe_(1/3) Sb_(2/3))O₃ --10 mole %

PbTiO₃ --43 mole %

PbZrO₃ --47 mole %

The mixture was calcined at 900° C. for 1 hour. A 0.3 weight % quantityof MnO₂ was added to the mixture and the resulting mixture was crushed,mixed and pressed in a mold and was sintered at 1280° C. for 1 hour.

SAMPLE B-3

The composition of Sample 3 (herein designated as B-3) of Table 1 of USP3,649,540 was prepared as a reference example. PbO, TiO₂, ZrO₂, Nb₂ O₅and Cu₂ O were mixed in a ball-mill in the following quantitiesindicated as mole percent.

Pb(Cu_(1/4) Nb_(3/4))O₃ --6 mole %

PbTiO₃ --44 mole %

PbZrO₃ --50 mole %

The mixture was calcined at 900° C. for 2 hours. A 0.5 weight % amountsof MnO₂ was added to the mixture and the resulting mixture was crushed,mixed and pressed in a mold and was sintered at 1200° C. for 1 hour.

SAMPLE RION NO. 13

The composition of sample Rion No. 13 (herein designated as Rion 13) ofGerman patent 2,001,290, was prepared as a reference example. PbO, TiO₂,ZrO₂ and Nb₂ O₅ were mixed in a ball-mill in the following quantitiesindicated as mole percent.

PbTiO₃ --43 mole %

PbZrO₃ --51.5 mole %

PbO--11 mole %

Nb₂ O₅ --5.5 mole %

The mixture was calcined at 900° C. for 1 hour and was crushed andpressed in a mold and was sintered at 1260° C. for 1 hour.

Samples of all compositions were shaped into discs having a diameter of30 mm and a thickness of 2 mm. A DC voltage of 3 KV/mm was appliedacross each sample disc for one hour in a silicon oil both at 100° C. topolarize the discs. The discs were kept for 24 hours after which timethe piezoelectric characteristics were measured as shown in Table 3below.

                  TABLE 3                                                         ______________________________________                                                                   Kp          grain size                             SAMPLE   ε/ε.sub.o                                                             tan δ                                                                             (%)   Qm    (μ)                                 ______________________________________                                        A-37      600    0.8%      58.0  1800  5.0                                    B-3      1000    0.7%      58.0  1850  6.5                                    Rion 13  1200    2.8%      60.0   100  7.8                                    2-13     1800    0.15%     74.5  2000  1.6                                    2-19     1550    0.2%      68.7  2400  1.8                                    ______________________________________                                    

The degrees of variation of the characteristics of μ, Qm, εV/ε and tan δdepending upon the change of terminal voltage applied to the productsare shown in Table 4.

                  TABLE 4                                                         ______________________________________                                               Terminal Voltage (V.r.m.s.)                                            (μ)   5       10       15     20     30                                    ______________________________________                                        Rion No. 13                                                                            0.8     1.5      2.0    2.1    2.1                                   B-3      2.0     4.0      6.1    6.8    7.2                                   A-37     3.5     6.4      7.9    8.0    8.1                                   2-1      3.4     6.3      8.2    9.5    10.5                                  2-2      3.5     6.4      9.6    12.2   16.5                                  2-3      4.0     8.0      12.2   16.3   23.9                                  2-4      4.2     8.4      12.5   16.7   25.0                                  2-5      4.9     10.0     15.5   20.3   28.8                                  2-6      4.4     9.0      13.2   17.8   26.5                                  2-7      3.5     6.5      9.8    13.2   17.5                                  2-9      5.5     11.0     16.5   22.0   31.2                                  2-13     5.0     10.1     15.4   20.6   30.8                                  2-19     5.3     10.3     15.6   20.8   31.0                                  ______________________________________                                    

                  TABLE 4'                                                        ______________________________________                                               Terminal Voltage (V.r.m.s.)                                            (Qm)     5        10       15     20     30                                   ______________________________________                                        Rion No. 13                                                                            250      195      165    140    120                                  B-3      560      340      290    250    210                                  A-37     600      320      220    190    180                                  2-1      300      300      225    210    200                                  2-2      700      650      550    450    380                                  2-3      860      710      670    600    560                                  2-4      870      745      680    620    580                                  2-5      900      810      720    660    610                                  2-6      900      770      660    610    550                                  2-7      730      585      490    470    370                                  2-9      970      820      750    700    650                                  2-13     910      800      720    670    620                                  2-19     930      810      730    680    630                                  ______________________________________                                    

                  TABLE 4"                                                        ______________________________________                                                  Terminal Voltage (V)                                                εvlε)                                                                     500       1000        1500                                        ______________________________________                                        Rion No. 13 16.5      too high    too high                                    B-3         6.5       20.0        38.5                                        A-37        5.0       15.0        24.5                                        2-1         8.0       23.0        43.0                                        2-2         3.0       8.0         14.8                                        2-3         2.5       5.1         7.6                                         2-4         2.1       3.9         5.7                                         2-5         2.0       2.8         4.0                                         2-6         2.2       4.0         6.0                                         2-7         3.1       9.2         17.5                                        2-9         1.7       3.3         5.0                                         2-13        2.0       3.7         5.7                                         2-19        2.1       3.8         5.8                                         (tan δ %)                                                               Rion No. 13 17.0      too high    too high                                    B-3         9.0       22.0        43.0                                        A-37        5.0       15.0        29.0                                        2-1         8.0       25.0        46.5                                        2-2         2.5       5.5         8.2                                         2-3         1.0       2.2         3.4                                         2-4         0.9       1.9         2.8                                         2-5         0.8       1.6         2.5                                         2-6         1.0       2.1         3.2                                         2-7         2.0       7.5         16.0                                        2-9         0.6       1.5         2.2                                         2-13        0.8       1.7         2.5                                         2-19        0.9       1.8         2.6                                         ______________________________________                                    

The dielectric constant and dielectric loss of each sample disc as afunction of terminal voltage (V) were measured as shown in FIGS. 2A and2B. It is apparent from these graphs that the dielectric loss and thedielectric constant of each of the reference samples (samples A-37, B-3and Rion 13) increase substantially with increasing terminal voltage.The sample designated as Rion 13 is especially poor in that atrelatively low terminal voltages, it experiences sharp increases in thedielectric constant and sharp dielectric losses. Sample 2-19 of thepresent invention, on the other hand, experiences very little change ineither dielectric constant or dielectric loss over the full range ofterminal voltage employed.

Samples of reference compositions A-37 and B-3 as well as a sample ofExamples 2-13 of the present invention were shaped into rings having thefollowing dimensions:

10 mm inner diameter

30 mm outer diameter

5 mm thickness

Two sheets of rings of each sample were bolt-fitted to a Langevintransducer which was used to measure the mechanical quality factor (Qm)as a function of terminal voltage by an admittance bridge as shown inFIG. 3. The amplitude (μ) of each sample was also determined as afunction of terminal voltage as shown in FIG. 4.

Referring to FIG. 3, it can be readily ascertained that referencecompositions A-37 and B-3 experience very substantial reductions intheir mechanical quality factors over the terminal voltage rangeemployed. On the other hand, sample 2-13 of the present invention doesnot experience nearly as much a loss in mechanical quality as the priorart samples, and in fact experiences only a rather moderate initial losswhich then tend to level off at rather substantial values.

Referring to the amplitude versus terminal voltage portion of FIG. 4, itcan be readily determined by just a casual inspection of the graph thatas the input voltage is increased upon one of the pyrochlore ceramiccompositions of the present invention, i.e. sample 2-13, the terminalvoltage correspondingly increases in a linear relationship throughoutthe range of amplitude versus voltage measured. Referring now to theplots for the two prior art compositions tested (A-37 and B-3) it can bereadily determined that the linear relationship which exists with thepresent composition does not exist with any of the prior artcompositions. Both prior art compositions only show an initial increasein the amplitude factor as a function of terminal voltage, but thanrapidly level off to a more or less constant amplitude value atincreasingly higher terminal voltages. These data clearly show thesuperior amplitude properties of the composition of the presentinvention which are clearly absent in all of the prior art compositions.

Having now fully described this invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit or scope of the inventionas set forth herein.

What is claimed as new and intended to be secured by letters patentis:
 1. A piezoelectric ceramic composition of the formula: x(Ba₂ Sb₂O₇)_(1/2).(1-x)[y(PbTiO₃)z(PbZrO₃)] wherein 0.01≦x≦0.07; 0.47≦y≦0.51;0.49≦z≦0.53 and y±z=1.0 and containing 0.1-1.0 wt.% MnO₂ and whereinsaid piezoelectric ceramic composition possesses a dielectric loss valuetan δ less than 0.3%, an electromechanical coupling coefficient Kp of60% to 74.5% and a dielectric constant ε value of 1000 to 1800 preparedby a process, comprising:individually forming lead titanate, leadzirconate and barium antimonate components by separately calciningmixtures of lead oxide-titanium oxide, lead oxide-zirconium oxide, andbarium oxide-antimony oxide; mixing said components with MnO₂ in anamount of 0.1 to 1.0 wt.% to provide a mixture in which said leadtitanate, lead zirconate and barium antimonate are present in amountsthat satisfy said formula; and sintering said mixture at a temperaturegreater than 1000° C. to form said piezoelectric composition.